1. Field of the Invention
The invention relates to a process for determining the starting capacity of the starter battery of a motor vehicle.
2. Description of the Related Art
To enable a starter battery to start a motor vehicle with an internal combustion engine, the state of charge and the degree of aging or the characteristic capacity loss are decisive, since the current intensity that can be taken from the starter battery and the power given off is limited by these factors.
In a modem motor vehicle, the properties of the generator, battery, and electricity-using devices are technically matched to one another in such a way that only in the case of massive malfunction can such a low battery charge state occur that the starting capacity or other functions are no longer assured. Therefore, the question of a reliable indicator for replacing the battery is of great interest. Especially if electricity-using devices that are relevant for safety such as electric brakes or electrically supported steering aids are installed, the knowledge of the predicted end of useful battery life is very important.
From German patent DE-C 3901680, a process for monitoring the cold starting capacity of a starter battery for an internal combustion engine is known in which the time curve of the voltage drop occurring during starting is observed and evaluated. The evaluation is performed on the basis of the limiting values of a characteristic line obtained by experience and as a function of the battery temperature.
Also known from German patent DE-A 2730258 is a device for indicating the state of charge of a vehicle battery which, in addition to the battery voltage and at least one other battery parameter, registers the engine temperature and gives a warning indication if the reading drops below a preassigned limit.
German patent DE-C 3712629 discloses a measuring device for the remaining service life of a motor vehicle battery which registers the battery voltage and the corresponding load current before and after the first starting process in the fully charged state of the battery, determines the temperaturecompensated internal resistance, registers it in a memory, and compares it with the internal resistances determined during later starting processes of the internal combustion engine. The indication is then given as a function of the preassigned stored threshold values.